The present invention relates to a die and a method of manufacture of the same to form a groove for mounting an optical part on a workpiece, a glass substrate which is produced with the said die and a method of manufacture of the same, and a method of pattern formation on glass substrate.
Up to now, methods of manufacture of glass elements by forming glass substrates by the press forming method have been used.
For example, to manufacture a substrate to mount an optical element (such as an optical fiber and a polarizer), a V-shaped groove (hereafter simply expressed as a V-groove) to position and dispose an optical fiber must be formed on a glass substrate, and in addition, the elements, such as a polarizer, must be disposed in the locations separated from the groove exactly by set distances.
To achieve this, a mask for photolithography is aligned with a glass substrate and, for example, tightly contacted with it. Then, by exposing them to ultraviolet light, a pattern in accordance with the mask pattern on the mask is formed. Thereafter, a Ti material or the like for forming devices is coated on the glass substrate, followed by etching treatment.
In this case, to accurately dispose the devices in the set locations, it is essential to align the glass substrate with the mask for photolithography with high accuracy. Therefore, it is necessary to provide an alignment marking on the glass substrate, such as a line, point, or other marking, to use as a reference for alignment with the mask for photolithography.
Conventionally, the V-groove itself formed on the glass substrate, i.e., the straight lines for the four sides forming the opening of the V-groove or the straight line in the deepest portion is used as the alignment marking, and by employing an aligner, the alignment marking on the glass substrate is aligned with the mask for photolithography. However, the edge portions of the opening of the V-groove are formed in a shape with a radial, rather than a sharp, cross section, and thus, they cannot be visually identified as straight lines for the four sides. In other words, the straight lines for the four sides in the opening portion of the V-groove offer poor visibility, and thus, it is difficult to align them with the mask for photolithography with high accuracy.
On the contrary, the straight line formed in the deepest portion of the V-groove offers satisfactory visibility since deepest portion has a sharp cross section. However, because the distance to the deepest portion of the V-groove is usually longer than the focal depth for the microscope in the aligner, it is difficult to align with high accuracy even if the straight line formed in the deepest portion of the V-groove would be used as an alignment marking.
Further, another difficulty is that the straight line (alignment marking) formed by the deepest portion of the V-groove and the marking provided on the mask for photolithography cannot be identified simultaneously, since the distance to the deepest portion of the V-groove is longer than the focal depth for the microscope in the aligner.
The present invention has been provided in consideration of these problems, and offers a die and a method of manufacture of the same, wherein a patterned die for forming grooves to mount optical parts on a workpiece is provided such that a pattern formed on the workpiece can be aligned with a mask for photolithography with high accuracy. Another purpose of the present invention is to offer a glass substrate and a method of manufacture of the same in which grooves having a substantially V-shaped cross section to mount optical parts are formed on the glass substrate, and the mask for photolithography can be aligned with high accuracy. Further, another purpose of the present invention is to offer a method of pattern formation on one principal surface of a glass substrate with which the mask for photolithography can be aligned with high accuracy.
The die according to the present invention is configured, comprising a first protrusion having a substantially triangular cross section on a pressing surface and a second protrusion having a length which is greater than a width thereof and a substantially trapezoidal cross section in planes extending through both length and width dimensions thereof. The first protrusion forms a groove having a substantially V-shaped cross section to mount an optical part on a workpiece, and the second protrusion forms a groove having a substantially inverse-trapezoidal cross section to provide an alignment marking on the workpiece.
By this, on a workpiece formed with the die, a groove having a substantially V-shaped cross section to mount (position and dispose) an optical part is formed, and at least one, more preferably two or more, grooves having a substantially inverse-trapezoidal cross section providing an alignment marking are formed. In other words, the second protrusion provided on the pressing surface of the die is formed in a substantially trapezoidal cross sectional shape, thus, when the shape is transferred to a workpiece, being inverted, a groove having a substantially inverse-trapezoidal cross section is formed in the workpiece. It is preferable that the inverse-trapezoidal groove has a depth within the focal depth for the optical inspection machine, for example, a depth of 1 to 20 xcexcm.
The edge portion of the bottom of this groove having a substantially inverse-trapezoidal cross section is sharp in cross section, and can be visually identified as straight lines for the four sides with clearness. Yet, the edge portion of the bottom of the groove is shallower than the bottom of the V-shaped groove, and thus within the focal depth for the microscope in the aligner.
Therefore, in an application where the workpiece is a glass substrate, in aligning the glass substrate with a mask for photolithography and forming a pattern on one principal surface of the glass substrate, if the inverse-trapezoidal groove is used as an alignment marking for aligning, the straight lines for the four sides constituting the bottom of the groove can be visually identified with clearness. The alignment marking and the marking on the mask can be visually identified simultaneously, thus, the glass substrate can be aligned with the mask with high accuracy. In this case, it is necessary to provide at least one groove having a substantially inverse-trapezoidal cross section as the alignment marking.
The groove having a substantially inverse-trapezoidal cross section providing the alignment marking can also be used as a marking to identify the orientation of the glass substrate. In this case, the direction of conveying and the state of disposition of the glass substrate can be electrically identified, and thus it is effective for full automation of the volume production system using the glass substrate.
Further, if any two of the straight lines for the four sides forming the bottom of the groove having an inverse-trapezoidal cross section are used as reference lines for positioning, alignment of the glass substrate with the mask for photolithography can be favorably performed. In addition, it is more preferable to provide a plurality of the grooves having an inverse-trapezoidal cross section as needed, and in correspondence with this, to provide a plurality of markings on the mask for photolithography. The groove having a substantially V-shaped cross section to mount an optical part on the glass substrate may be provided for the number corresponding to the required number of optical parts to be mounted.
Next, with the method of manufacture of a die according to the present invention, in manufacturing the die from the base material by grinding, the first protrusion to form a groove having a substantially V-shaped cross section and the second protrusion to form a groove having a substantially inverse-trapezoidal cross section are simultaneously provided in die manufacturing. By this, compared to a case where the alignment marking is provided on the glass substrate separately from the groove having a substantially V-shaped groove, the distance between the groove having a substantially V-shaped groove and the alignment marking can be set with high accuracy, and the number of production steps is reduced. Further, when a photodiode or a laser diode is fixed on a glass substrate as a device to mount an optical element (hereafter expressed as a substrate for mounting) separately from the pattern formation, by using a die according to the present invention, the distance between the fixing location of the photodiode or the laser diode and the location of a groove having a substantially V-shaped cross section where an optical fiber is mounted can be determined with high accuracy.
With the method of fixing the above stated photodiode or laser diode on a glass substrate, a plurality of substrates for mounting are formed simultaneously on a glass substrate having fixed dimensions, and then the glass substrate is divided to obtain individual substrates for mounting. If, however, a photodiode or a laser diode was not previously fixed on the glass substrate before division, a photodiode or a laser diode can be fixed on the individual substrates after dividing the glass substrate. In this case, electrode patterns for fixing the photodiode or the laser diode thereon and marks corresponding to the electrode patterns are drawn on a mask for photolithography, and thus, positioning the photodiode or the laser diode can be performed favorably.